Clemens, in U.S. Pat. Nos. 3,842,194, 3,842,217 and 3,909,517, discloses a capacitive information recording and playback system. In this system disc record replicas can be prepared having geometric variations in a spiral groove in a disc surface which represents information such as a video signal. These discs are made of plastic and coated with a thin layer of metal and a thin layer of a dielectric material. A stylus having a conductive electrode completes the capacitor and is used to reconstitute the information as an electrical signal.
Further developments in this area have produced an information disc record replica made of a conductive plastic material. Other systems based on a capacitance readout have an information track wherein geometric variations are impressed in the surface. In either the grooved or the nongrooved system the conductive disc is fabricated from a molding composition containing submicron-sized carbon particles which impart sufficient conductivity to the disc record for capacitive readout.
In order to analyze the products which result from these molding compositions it is sometimes required to remove the submicron carbon particles such as carbon black. Their small particle size, generally the particles have a diameter in the range of a few hundred angstroms, does not allow separation of the particles by ordinary means.